1. Field of the Invention
The invention relates generally to an apparatus and method for stimulating reservoirs, such as vessels, barges, mud tanks, storage tanks, holds, other storage units, and flow lines using heated liquid injections. More particularly, the invention relates to an apparatus for stimulating reservoirs, vessels, tanks, holds, other storage units, or flow lines by injecting therein heated fluids under pressure and a method of stimulating reservoirs using such apparatus. As used in this application, a reservoir can be a tank used for collecting and storing a liquid, a receptacle or chamber for storing a fluid, a receptacle or chamber for holding a liquid or fluid, a subterranean accumulation of oil or gas held in porous and permeable sedimentary rock (reservoir), a wellbore, a pipeline, or an underground accumulation of petroleum or natural gas.
In the exploration and development of hydrocarbon reservoirs, a well is drilled to a subterranean reservoir, and thereafter, a long string of tubing segments is placed within the well to allow the production of hydrocarbon fluids and gas. During the production phase, paraffin, asphaltines, and other sediment from the surrounding formation settle on the inner surfaces of the production tubing and restrict the fluid flow to the surface. Further, the perforations formed in the wellbore reservoir may become gradually plugged and/or damaged by drilling fluids, sediment, and the like. Once the reservoir becomes damaged, the operator needs to stimulate the reservoir, which is often done with the injection of chemical compounds into the tubing extending in the wellbore. Sometimes, the liquid injection compounds are heated before introduction into the wellbore to facilitate removal of the clogging material from the tubing. Sometimes, the reservoir is stimulated using diesel, other times—using an acidizing material, such as formic acids and other stimulation fluids such as water and hot oil.
In the past, in order to heat these types of compounds, operators could employ an open flame. However, recent governmental government regulations prevent the use of an open-flame heater in an oil- and gas-production environment. Thus, there exists a need for a thermal fluid unit that is capable of heating a reservoir stimulation compound without the need for having an open flame.
2. Description of Related Art, Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Apparatus and methods exist to clean or treat reservoirs. In the broadest sense, a reservoir is a vessel, tank, hold, other storage unit, or a pipeline or other flow line. Apparatus and methods for cleaning reservoirs in this broad sense can include apparatus and methods that inject, under pressure, a cleaning, dispersing, treating, neutralizing, or stimulating agent into the reservoir. Methods for cleaning or treating reservoirs include applying heated fluid or chemicals under pressure to loosen, disperse, or dissolve “contaminants.” The particular working materials (that is. the composition of the fluid), the temperature of the working materials, and the pressure at which the working materials are introduced into a reservoir depend on the characteristics of the contaminant, which can vary from reservoir to reservoir.
Particular working materials can include, among others hot water, either fresh or salt, gun barrel water (also mown as produced water) heated diesel fuel, heated produced oil, raw chemicals (such as xylene or benzene, either with or without water or diesel oil or heated oil), or heated chemicals. Selecting particular working materials depends significantly on the particular characteristics of the “contaminant” and on the particular application. Applications can include, among others, down hole oil wells or gas wells, vessel storage tanks, vessel holds, pipelines, pig traps, storage tanks, holding tanks, and towers (such as cat crackers, fractionation towers, and emulsifiers). Selection of appropriate temperature and pressure also depends on the application.
European patent No. 032813 describes a process for the removal of sludges from crude or refined oil storage tanks by injecting a dispersing agent into the sludge by means of a water jet. The emulsified oil fractions are removed under pressure and recirculated to the jet. The sludge is physically and chemically altered so that it can be pumped and easily removed from the tank, the emulsion being further mixed to an oil volume sufficient to cause the sludge separation, the water layer being separated and the heavy hydrocarbons recovered.
Japanese publication No. 558030398 describes the treatment of sludges by adding an amount of solvent and heating by circulating in the oil furnace to extract paraffin waxes and separating solid constituents from the oil fraction.
The so-called T.H.O.R. process is a mechanical system for the recovery of hydrocarbons from the oil sludge and contaminated oil tank bottoms. The process involves penetrating the sludge bulk with a hot water circulating system using a submersible pump. The T.H.O.R. process comprises two stages: sludge moving and sludge refining. To render the sludge mobile, water heated with refinery steam is pumped into the tank to lower the viscosity of the sludge so as to optimize its pumping and recovery. The mobile sludge is pumped through a submersible pumping unit placed in the medium to be pumped. The amount of water placed into the tank is equivalent to that of the sludge to be moved. The water is kept circulating during the whole liquefaction period of the tank contents, which normally takes 1 to 8 days. The pumping process has a maximum flow rate of 15000 liters per hour, the mass being pumped corresponding to a ratio of 50% water/50% sludge. The mixture is pumped through Alfa Laval equipment for the removal of insoluble foreign matter and water so as to produce oil to be reintroduced in the refining process. The recovered product, of BSW lower than 1% and low conductivity, is mixed to crude oil in predetermined amounts. The so-called “SUPERMACS” system developed by Riedel Environmental Technologies Inc. employs heated water jets under high average pressure in order to melt and heat paraffin and sludge deposits. The products are separated and recovered based on their different densities, the oil contained in the sludge also being recovered.
U.S. Pat. No. 5,580,391 discloses a process for the thermochemical-cleaning of a sludge-containing storage tank for petroleum oil or a similar material which comprises: adding to the sludge in the tank an organic solvent or mixture of solvents which fluidizes the sludge, the volume ratio of solvent:sludge being in the range of 0.5:1 to 2.5:1; adding to the mixture of sludge and organic solvent an aqueous nitrogen-generating system comprising a reducing nitrogen salt, an oxidizing nitrogen salt and an acid activator which interact to generate nitrogen and heat, thereby causing thorough mixing of the sludge, the solvent, and the aqueous nitrogen-generating system; allowing the contents of the tank to separate to form an oil phase consisting essentially of the solvent and the organic constituents of the sludge, a saline aqueous phase comprising the residue of the nitrogen generating system, and, if present, the solid inorganic constituents of the sludge; removing the oil phase and recovering the solvent and other valuable constituents therefrom; removing the aqueous phase and sending it to effluent treatment; and if required removing also any solid inorganic residue remaining in the tank. In this process sludges of crude or refined oil, stored in tanks or any other kind of container, are fluidized and the oil contained therein is recovered by the addition of a solvent having the correct properties to fluidize the sludge, followed by the addition of aqueous solutions of inorganic salts that generate nitrogen and heat.
Considering that an offshore platform presents special challenges to accommodating large systems for stimulating wells and clearing the down-hole perforations, there exists a need for a compact apparatus that can supply pressurized heated liquid to break down paraffin and open up the production lines. The present invention contemplates provision of such a system and a method of providing a heated compound for stimulating a reservoir using a self-contained unit that has a relatively small footprint.